This application in general relates to an improved sprag clutch. More particularly, the present invention relates to an improved sprag and retainer combination that is inexpensive to manufacture and assemble.
Sprag clutches are well known and utilized in various applications. In such clutches, an outer race is connected to a first shaft and an inner race, received at the inner periphery of the outer race, is connected to a second shaft. A plurality of sprags are pivotally received between the inner and outer races to selectively transmit rotation between the two.
Typically, a retainer ensures that each of the plurality of sprags is properly positioned between the circumference of the inner race and the outer race. These retainers extend beyond the axial extent of the sprags, and typically include notches through which the sprag extends. The retainer must contact the sprag at a minimum contact point radially inwardly in a direction towards the inner race in order to properly mount the sprags for pivotal movement. The minimum contact point varies with a particular sprag geometry, and the calculation of the contact point is within the skill of a worker in the art. The retainer typically has a portion radially outwardly of this minimum contact point to provide concentricity to the retainer. Typically, the retainer extends radially outwardly to a position adjacent the inner periphery of the outer race.
Retainers are typically formed from a cylindrical member, with notches punched through the thickness of the cylindrical member at a central position. Retainers must be of a certain minimum thickness at the axial ends, or the punching of the notches through the axial center of the retainer deforms the axial ends. In many prior art retainers the retainer is formed of a minimum thickness that is of the size required at the ends throughout its axial extent. This is undesirable since it results in bulky retainers which require a large amount of material and are relatively expensive.
In one prior art retainer, a relatively thin tubular member has ends bent radially inwardly to define thicker end portions. The radially inwardly extending ends result in thick portions at the axial ends to resist deflection when notches are punched in the center of the retainer.
Such retainers are widely used, however, some deficiencies exist with this type of retainer. As mentioned above, there is a certain minimum contact point for contact between the retainer and the sprag members, and there is preferably a portion of the retainer radially outward of this point. Since the legs in the above-discussed retainer extend radially inwardly from the notches, it is sometimes difficult to achieve the minimum contact point between the retainer and the sprags, and also to have a portion radially outward of the minimum contact point. In some prior art retainers, the center portion of the retainer is curved radially inwardly to define a groove centered above a central axis of the retainer. A center of the retainer does contact the sprags at the minimum contact point, while other portions are disposed radially outward. The ends extend radially inwardly beyond the minimum contact point. Forming the center with this complicated cross-section is, however, undesirable.
Sprag members typically have notches formed at each axial end to receive springs that extend throughout the circumference of the clutch member. The springs urge the sprags to a first pivoted position. The use of the two notches may undesirably complicate the manufacture of the sprag.
In response to this problem, some prior art clutches may have utilized sprags which have a single central notch at an inner periphery to receive a single spring. This results in a sprag that is less complicated than the above-discussed sprags, however, these sprags are sometimes difficult to mount, and often required other structural features to provide an adequate mount. In one known sprag that has a center notch, a central bearing notch is formed at an outer periphery. This bearing notch provides additional guidance to the sprag. The requirement of forming this additional bearing notch in the outer periphery, however, eliminates one benefit of using a central spring notch, namely reducing the number of notches in the sprag. Further, this bearing notch at the outer periphery reduces the contact area between the sprag and the inner periphery of the outer race, which is also undesirable.